This application claims priority from Japanese Serial No. 11-083607, filed Mar. 26, 1999.
1. Field of the Invention
The present invention relates to a pavement marking article and, more particularly, to a pavement marking article capable of affording retroreflection in wet or rainy weather as well as dry conditions. The present invention also relates to a process for producing the pavement marking article.
2. Background of the Invention
A pavement marking article is provided at a predetermined portion on a road, for example, at a center line or pedestrian crossing. In a conventional pavement marking article, visibility in the nighttime may be provided by providing transparent microspheres for retroreflection on the surface. The transparent microspheres are usually attached to the substantially flat surface of the pavement marking article to form a retroreflective pavement marking article. However, conventional retroreflective marking article may have the drawback that retroreflection is lowered in rainy weather. Because water adheres to the transparent microspheres of the pavement marking article in the rain so that the direction of light, which is incident upon the reflected surface of the microspheres, is changed and desired reflection of light is not obtained. It has been confirmed that the direction of light is markedly changed when the transparent microspheres are covered with water. Accordingly, it is desirable that water be removed from the transparent microspheres.
To remove water from the transparent microspheres, various attempts have been made. For example, Japanese Unexamined Patent Publication (KOKAI) No. 3-224903 discloses a pavement marking article comprising a pavement marking substrate having a lot of pores. This pavement marking substrate has rainwater permeability because of its pores. Accordingly, water accumulated on the surface of the pavement marking substrate or pavement marking article is absorbed by the pores on the road surface, thereby to flow away.
Japanese Unexamined Patent Publication (KOKAI) No. 9-41331 discloses a pavement marking article configured as a marking line having a regular or irregular triangle or hexagon as a basic shape in the cross section of the road in the width direction, said marking line being a broken line to act as a waterway which makes it possible to conduct prevention of flooding and retroreflection. That is, this pavement marking article is intended to remove water along its inclined portion and waterway.
Furthermore, Japanese Unexamined Patent Publication (KOKAI) No. 7-197407 discloses a pavement marking article comprising a lustrous material (glass beads) having light scattering and retroreflection properties fixed on the surface in the raised form. That is, this pavement marking article makes it possible to prevent the whole article from covered with water by making the lustrous material protrude.
Similar to this publication, Japanese Unexamined Patent Publication (KOKAI) No. 6-330510 also discloses a pavement marking article wherein plural convex-shaped microspheres having transparent microspheres are provided on the surface at a predetermined distance to prevent the whole convex-shaped microspheres from being covered with water.
Japanese Unexamined Patent Publication (KOKAI) No. 6-280221 also discloses a pavement marking article wherein an irregular pattern is formed alternatively on the surface on which transparent microspheres are fixed to prevent the whole transparent microspheres from being covered with water on wetting.
Regarding the pavement marking articles described in the above publications, the effect of removing water is expected. In the case of these pavement marking articles, however, water can not be removed completely from the surface thereof, because water remains as a water film on a part of the surface of a usual pavement marking article and, as a result, water adheres to the transparent microspheres. Accordingly, retroreflection is lowered by the presence of water and visibility of the pavement marking article in case of rainy weather is deteriorated compared with the case of fine weather.
On the other hand, a pavement marking article disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 9-279516 comprises glass beads having a refractive index of 1.9 to 2.5, which is higher than that of the above transparent microspheres used for the purpose of removing water. Such glass beads having high refractive index can correct the direction of light so that it can afford retroreflection even if water adheres thereon in case of rainy weather.
Generally, the glass beads having a refractive index of 1.9 to 2.5 are liable to be broken because of comparatively low hardness. The above publications disclose that these glass beads have a particle diameter of 106 to 850 xcexcm and are uniformly provided with protruding in the largest degree on a comparatively flat crude surface. Accordingly, when the glass beads are provided with protruding in the largest degree, as described above, the pavement marking article is liable to receive an impact frequently by comings and goings of automobiles and pedestrians and, therefore, the shape can not be retained only a comparatively short period of time. As a result, this marking article can not afford retr6reflection for a long period of time.
The present invention seeks a pavement marking article capable of affording retroreflection in wet or rainy weather.
According to one aspect, the present invention provides a pavement marking article comprising a substrate, a plurality of protrusions provided on the surface of the substrate, and first transparent microspheres having a refractive index of not less than 2.0 fixed at least on the surface of the substrate between adjacent protrusions.
According to another aspect, the present invention provides a process for producing a pavement marking article comprising a substrate, a plurality of protrusions provided on the surface of the substrate, and first transparent microspheres having a refractive index of not less than 2.0 fixed at least on the surface of the substrate between adjacent protrusions, which comprises the steps of molding a material capable of being thermally plastically deformed, thereby to form a substrate; preparing a molding die with a plurality of through openings, and coating the first transparent microspheres having a refractive index of not less than 2.0 on at least the surface of the molding die; and pressing the surface coated with the transparent microspheres of the molding die against one surface of the substrate, thereby transferring the first transparent microspheres to the substrate with forcing a part of the substrate into the openings of the molding die.